This invention is in the field of protective devices for photo-detectors, and is particularly concerned with protecting such detectors against laser countermeasures. The types of detectors being protected include image intensifiers, television camera tubes, infrared detectors, and the human eye. Of these, the human eye requires the greatest protection because of its low damage threshold. Various techniques have been used and suggested for use against laser (or other possibly damaging radiations, such as sunlight). The main techniques used are fast-acting shutters (mechanical or electro-optical) and interference filters (absorbing or reflecting).
Unfortunately, these techniques have disadvantages which make them unusable for some detectors. Specifically, shutters require relatively long times to open and close, compared to the rise time of a pulsed laser. Interference filters, in order to block the spectra of various lasers, must be individually made for each threatening laser, and stacked in front of the detector being protected. For detection of low-level light, such stacked filters present unacceptable attenuations. The instant invention overcomes these disadvantages; it is fast acting and relatively non-attenuating in its unactivated mode.